Introduce a SignatureData class so that signature functions can store both their

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 7c9732024593b3ff36259482a9b9cb17f9206edf..8cf284d8107bfafacc8001314c8d91536a14720c 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -22,6 +22,7 @@ namespace dart {
   V(PatchClass)                                                                \
   V(Function)                                                                  \
   V(ClosureData)                                                               \
+  V(SignatureData)                                                             \
   V(RedirectionData)                                                           \
   V(Field)                                                                     \
   V(LiteralToken)                                                              \
@@ -867,6 +868,23 @@ class RawClosureData : public RawObject {
 };
 
 
+class RawSignatureData : public RawObject {
+ private:
+  RAW_HEAP_OBJECT_IMPLEMENTATION(SignatureData);
+
+  RawObject** from() {
+    return reinterpret_cast<RawObject**>(&ptr()->parent_function_);
+  }
+  RawFunction* parent_function_;  // Enclosing function of this sig. function.
+  RawType* signature_type_;
+  RawObject** to() {
+    return reinterpret_cast<RawObject**>(&ptr()->signature_type_);
+  }
+
+  friend class Function;
+};
+
+
 class RawRedirectionData : public RawObject {
  private:
   RAW_HEAP_OBJECT_IMPLEMENTATION(RedirectionData);